I look at it this way, any 25~ year old car will have issues no matter what brand it is. The issues with the E30 are commonly known and once fixed quite reliable. That's why I advised you one with repair history would be a good idea. That way you know what's been repaired or replaced. These cars are great to learn on! Their not as complicated as everyone makes them out to be. Just a different engine design then the norm. Still function the same way.
The biggest problem with the E36 is the cooling system. The plastic components were known to become brittle and crack causing overheating. These are all parts that are easit replaceable for not large amounts of money. I had my water pump replaced in 2006-07 and I have never had an issue with it since. Pre 1997 the water pump was plastic and broke over time. Their was no issue of bad head gasket in any model uear unless you overheated the car and blew it.
The complete list of parts needed to overhaul a cooling system is the following:
- Thermostat housing (aluminum)
- Water pump (aluminum impeller, Stewart brand is the best)
- Fan clutch and fan
- Upper and lower radiator hoses
- Coolant expansion tank
This is the same on any car really, but te need for it can be more prevalent in the E36.
These cars are fantastically well designed and last a very long time as long as properly cared for. I would advise you to see and download the copies of the service manuals posted at the top of the E30 and E36 sub forums. Reading through those will for you an excellent idea of how to fix things should they go wrong, and which model might suit your skills and abilities better.
Here is a link to what is covered in the Inspection I & Inspection II services (what BMW calls their service packages):
You are right about the 90's ones being the best. They were designed to be perfectly balanced for handling. Their was a reason BMW is called The Ultimate Driving Machine. People fall in love with these cars because of the wonderful driving experience. Their the only cars I will ever own (not counting my truck).